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RE: "<font size=-1>Additionally, to keep costs down, I would let the VFD
control the situation, not the EMCS. Just have the VFD update the
EMCS, and allow the EMCS to reset the differential pressure sensor."</font><font size=-1></font>
<p><font size=-1>I do not agree with this concept. Using stand alone
VFD control loses the integrated features of a building DDC system.</font>
<br><font size=-1>-How does one adjust and tune the VFD static pressure
control?</font>
<br><font size=-1>-How does one deal with PID windup problems?</font>
<br><font size=-1>-When the system is commissioned, establishing the correct
static pressure control setpoint will be VERY difficult without DDC access
to VAV box damper positions.</font><font size=-1></font>
<p><font size=-1>The cost to control a VFD from the building DDC system
will actually be less when the VFD is connected to the DDC system using
modBUD or LON network... you only run one data cable from DDC controller
to the VFD, and you pick up all 60 or so VFD data points, some of which
are quite useful for diagnostics and monitoring energy use.</font>
<br><font size=-1></font>
<dl>
<dd>
<font size=-1>Thomas E. Anderson</font></dd>
<dd>
<font size=-1>President</font></dd>
<dd>
<font size=-1>Cx Associates, Ltd.</font></dd>
<dd>
<font size=-1>Building Commissioning Specialists</font></dd>
<dd>
<i><font size=-1><a href="http://www.cx-assoc.com">http://www.cx-assoc.com</a></font></i></dd>
<dd>
<i><font size=-1>933 Road 101</font></i></dd>
<dd>
<i><font size=-1>Jeffersonville, Vermont 05464 USA</font></i></dd>
<dd>
<i><font size=-1>hvac@cx-assoc.com</font></i></dd>
<dd>
<i><font size=-1>Tel: 802-644-5616 Fax: 802-644-6797</font></i></dd>
</dl>
<font size=-1></font>
<p>"Kirchhoff, Eric" wrote:
<blockquote TYPE=CITE>
<p><font size=-1>Although I have always been interested in designing such
a system I have yet to do so. However, that doesn't seem to stop
me from adding in some anecdotal information from friends who have designed
such systems. First off (not from friends, this is my own observation),
a VFD for an air handler tends to be nearly the same cost as a starter,
except for the additional control point-that being the differential pressure
sensor. Additionally, to keep costs down, I would let the VFD control
the situation, not the EMCS. Just have the VFD update the EMCS, and
allow the EMCS to reset the differential pressure sensor. Go ahead
and monitor all the points you want, and at least do start / stop, status,
and DP sensor reset. Like Robert says, the VFD is a cost wise investment,
even if you end up later on setting it up to be a constant speed system,
the cost risk is low.</font>
<p><font size=-1>Now I would like some additional information. The
IRR of 30% to 50%; is that just for the mechanical investment or everything?
Since this type of system uses a raised floor system, all the utilities
end up running under the floor. Code will dictate the use of plenum
rated cable (even when run inside conduit), the floor system itself tends
to be proprietary-or at best limited in number of suppliers--hence supply
and demand comes into play driving the cost of the floor up and that is
beyond the fact that it is already more expensive since it needs to be
structurally capable of carrying the loads (including areas for very large
filing systems), there are a limited number of suppliers of underfloor
vav systems (and the quality varies), as a positive there is a greatly
reduced amount of sheet metal used for ductwork, there usually is not a
realistic coordination between cubical / office layout and diffuser placement
(in large jobs, the eventual leasee is unknown hence their layout needs
are unknown) causing problems by a maintenance staff that is unfamiliar
with the system (despite training), and another maintenance problem are
users who do not understand nor properly utilize the system hence they
will block the diffusers (more often then the overhead type). Plumbing
may also be run in the floor space as well as other utilities causing a
need for additional wall furrings then may be in a more traditional layout.
Was there any account of these items in the IRR, or was it a theoretical
value based only on the mechanical components?</font>
<p><font size=-1>I do not mean to discourage anyone from using this system,
I actually am very interested and excited to implement this type of system,
and believe (instinctually) that it is an energy efficient alternative
to the traditional diffusion method of airside systems. The points
listed above are things you should be aware of, and are questions to ask
so as to minimize their impact.</font>
<p><font size=-1>As Rob says Good Luck, and have some fun!</font>
<p><font size=-1>Eric Kirchhoff, PE</font>
<p><font size=-1>-----Original Message-----</font>
<br><font size=-1>From: Robert Lord [<a href="mailto:rgl.lsbris@lincolne.com.au">mailto:rgl.lsbris@lincolne.com.au</a>]</font>
<br><font size=-1>Sent: Sunday, November 03, 2002 2:55 PM</font>
<br><font size=-1>To: bldg-sim@gard.com</font>
<br><font size=-1>Subject: [bldg-sim] VAV control of underfloor air</font>
<p><font size=-1>A typical design is to zone the floor compartment according
to aspect and allow the individuals to adjust the swirls.</font>
<br><font size=-1>There are only a handful of large VAVs and the fan speed
is varied according to duct static pressure (not plenum pressure).</font>
<p><font size=-1>In most instances, I have found that the internal rate
of return is between 30% & 50% and hence is a good investment. I am
sure VSD pricing and energy pricing varies but a point to note is that
the RH control is improved.</font>
<p><font size=-1>Good luck!</font>
<p><font size=-1>Rob Lord</font>
<p><font size=-1>-----Original Message-----</font>
<br><font size=-1>From: Molinini, Louis [<a href="mailto:lmolinini@syska.com">mailto:lmolinini@syska.com</a>]</font>
<br><font size=-1>Sent: Saturday, 2 November 2002 8:37 AM</font>
<br><font size=-1>To: bldg-sim@gard.com</font>
<br><font size=-1>Subject: [bldg-sim] VAV control of underfloor air</font>
<p><font size=-1>Do any of you out there have any experience designing
an underfloor air</font>
<br><font size=-1>system with VAV control. The particular system
I am looking at is a plenum</font>
<br><font size=-1>based system with manually adjustable swirl diffusers
(Titus/Krantz). I am</font>
<br><font size=-1>curious if it ends up operating like a constant volume
system or is it worth</font>
<br><font size=-1>the expense of installing the freq drive and the Static
pressure sensor or</font>
<br><font size=-1>differential pressure sensor. Any help is greatly
appreciated.</font>
<br><font size=-1>Thanks,</font>
<br><font size=-1>Louis</font>
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